Closely-linked mutations affect meat production in pigs

Apr. 9, 2010 - Complex interactions between DNA mutations affect physical traits of pigs, according to data reported online in the Journal of Animal Science. Researchers from the University of Bologna, Italy and Italy’s National Association of Pig Breeders analyzed pig DNA and found that two different mutations influence fatness and muscle deposition in swine.

DNA of specific pigs and their siblings was tested to see if there was a connection between the closely linked mutations and physical traits. Previously, a specific mutation affecting muscle mass and fat deposition (IGF2 intron3-g.3072G>A) was located on the second chromosome in pigs, so they used a technique called linkage mapping to determine if another mutation that also affects meat production (cathepsin D [CTSD]) was nearby on the chromosome in Italian pigs. Scientists knew that CTSD had an affect on the production traits ( e.g., body weight gain, lean cuts, and ham weight), of pigs, but they questioned whether IGF2 could also play a part.

They tested for mutations in Italian large white pigs and Italian Duroc pigs, and found that the IGF2 mutation did have a strong link to meat, carcass, and production traits in both breeds. Despite the association, the link was not significant enough to establish the IFG2 mutation as the cause of the physical traits. These findings confirm previous data from other researchers. The research team emphasizes that it is unclear whether CTSD mutations are responsible for traits like larger muscle mass or if another gene close by on the chromosome is responsible.

The project reveals the complexity of genetic testing. The researchers found the IGF2 mutation in pigs more often than they predicted. They hypothesize that the IGF2 mutation can be “de-repressed” (when a normally inactive gene is activated), or perhaps DNA replication during chromosome production in the parent pig causes the mutation to become more common. The IGF2 mutation is already used by scientists and pig breeders who rely on markers in genes to select pigs, so the researchers suggest adding information from the CTSD genotype to increase selection efficiency.

In addition to its importance in pig breeding, research into CTSD is also significant to human genetics. CTSD exists in both humans and swine, and it has been associated with cell death, protein degradation, and Alzheimer’s disease in humans.

The researchers suggest that future studies should investigate the link between CTSD and IGF2 mutations in other breeds of pig.

The study was funded by the Italian MiPAAF SelMol project. The paper, entitled “The IGF2 intron3-g.3072G>A polymorphism is not the only SSC2p mutation affecting meat production and carcass traits in pigs: evidences from the effects of cathepsin D (CTSD) gene polymorphism” can be found in full at journalofanimalscience.org.

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Madeline McCurry-Schmidt
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